17" Tyre Pressure

[Jasonn]

Evening all,

Went out last week in the rain and noticed zed was very squirrely with the traction light coming on.

She was MOTd when I bought her, no advisories and new Bridgestone RFTs on the front. In the year I've had her she's done probably 5k (if that) so when I looked over the tyres, they're past their wear indicators so I'm picking up Goodyear Assy 5s tomorrow for each corner (good price £300 Inc fitting from a local franchise).

Question is what pressures should I be looking at?


The RFTs seem to run fairly high pressures when I remember my old capri running on 28psi and my MG on 32psi

 

[Anonymous]

I run 32/34 through to 34/36 PSI that is not Bar!

Thats on Conti Sports Contacts on Team Dynamics Pro Race 1.2 wheels 235/45 17 on front and 255/40 17 on rear 8J front 9J rear

Ran similar pressure on Coni TS850 winter tyres on 17" BMW 103 Daisys 225/45 17 all round

 

[flybobbie]

I ran 38 front and 42 rears on 17 and now 18, although now i run 40 rear having seen the slight crown wear on 42 rear. My tyres show very little wear after 25k front and 20k miles rear. GY asym 3's. Depends which car you have. My 23i.

Often wonder the effect of atmospheric pressure when checking. I fitted some tyre pressure monitors to aircraft tyre, they do increase a few psi when at altitude. So looks like tyres pressures should be set when the atmosphere is standard temp. and pressure.

 

[rdm05z4]

Must be a UK thing. All our tyre's over here in the States come stamped with manufacture's recommended pressure. We don't have to Guess.

 

[Lazza]

Must be a UK thing. All our tyre's over here in the States come stamped with manufacture's recommended pressure. We don't have to Guess.

We have maximum pressure on the tyre. How can the recommended pressure be on the tyre? It depends on the car they are fitted on. Even different models of the same car can require different pressures!

 

[Silverstar]

Must be a UK thing. All our tyre's over here in the States come stamped with manufacture's recommended pressure. We don't have to Guess.

We have maximum pressure on the tyre. How can the recommended pressure be on the tyre? It depends on the car they are fitted on. Even different models of the same car can require different pressures!

I think he might be referring to the label in the door jamb which tells you the recommended pressures?

 

[flybobbie]

GY asy 2 is around 50psi. plenty of scope for experimentation.

 

[mcbutler]

Must be a UK thing. All our tyre's over here in the States come stamped with manufacture's recommended pressure. We don't have to Guess.

That is a really good comment, pot luck guessing at your tyre pressures is not a good idea.
I asked Michelin for comment when I replaced my Bridgestone RFT's with Pilot sport 4s. They referred me to a supplier who said (in a nutshell) The primary (not the only) factor affecting the pressure is the tyre width. Adequate pressure to ensure the entire tread width is in equal contact with the road surface is the primary concern. So, stick with your current pressures and if you want to (i do) measure the tread across the width of the tyres every 1000 miles. If your wear is equal the pressures are correct. I run my tyres on original RFT pressures, wear is spot on...

 

[Ewazix]

GY asy 2 is around 50psi. plenty of scope for experimentation.

Umm this could be read two ways, I want to see the video if you are going to use 50 psi a a point for experimentation!

50 psi is the maximum it can take, not a recommendation. I used the label pressures and experimented up and down a few psi when I was on 17" Non-RFT's

 

[brillomaster]

we dont have to guess - the manufacturer says the recommended pressures on the placard, wherever that is.

i believe this is a E89 z4.

 

[Silverstar]

Must be a UK thing. All our tyre's over here in the States come stamped with manufacture's recommended pressure. We don't have to Guess.

That is a really good comment, pot luck guessing at your tyre pressures is not a good idea.
I asked Michelin for comment when I replaced my Bridgestone RFT's with Pilot sport 4s. They referred me to a supplier who said (in a nutshell) The primary (not the only) factor affecting the pressure is the tyre width. Adequate pressure to ensure the entire tread width is in equal contact with the road surface is the primary concern. So, stick with your current pressures and if you want to (i do) measure the tread across the width of the tyres every 1000 miles. If your wear is equal the pressures are correct. I run my tyres on original RFT pressures, wear is spot on...

+1 I have kept the pressures as indicated on the label and over 3 to 5000 miles the wear is pretty even across all the tyres.

 

[rdm05z4]

Guys, It was a joke. Guess our types of humor are different. I Know in the door jam manufacture places recommended pressure given the type of car and spec's. They are their for recommended safety use. And yes if you replace rims or tires you will need to rethink the pressure.

 

[Jasonn]

Thanks for the info guys - I've gone with the RFT pressures and I'll ease them off gradually once the new rubber has settled a bit.

Garage had me worried at the start when they confirmed the online order then asked me to confirm that all tyres were the same size as "Z4s have staggered tyre sizes" - after reassuring him he wanted to just check at which point got the "ahh it's the new shape", then... "these are RFTs on the car, you've order non RFT" - anyway after explaining why I don't want RFT anymore the car was driven away onto the ramp - took them just over an hour.

Went to collect the invoice and had a chat with the manager who said that potenzas are probably the worst tyre for Z4s and a lot of 3 series come through and have them taken off.

The 2 mile journey home was a revelation... Car seems quieter on concrete roads, no crashing over speedbumps, can't wait to let these tyres bed in so I can see whether the grip is better.

I can't believe how bad RFTs are, I'd never have changed to non RFTs unless I'd read this forum - massive thanks to the members and admins